Total synthesis,structural, and biological evaluation of stylissatin A and related analogs

The natural product cyclic peptide stylissatin A ( 1a ) was reported to inhibit nitric oxide production in LPS‐stimulated murine macrophage RAW 264.7 cells. In the current study, solid‐phase total synthesis of stylissatin A was performed by using a safety‐catch linker and yielded the peptide with a trans‐Phe⁷‐Pro⁶ linkage, whereas the natural product is the cis rotamer at this position as evidenced by a marked difference in NMR chemical shifts. In order to preclude the possibility of 1b being an epimer of the natural product, we repeated the synthesis using d ‐allo‐Ile in place of l ‐Ile and a different site for macrocyclization. The resulting product (d ‐allo‐Ile²)‐stylissatin A ( 1c ) was also found to have the trans‐Phe⁷‐Pro⁶ peptide conformations like rotamer 1b . Applying the second route to the synthesis of stylissatin A itself, we obtained stylissatin A natural rotamer 1a accompanied by rotamer 1b as the major product. Rotamers 1a , 1b , and the epimer 1c were separable by HPLC, and 1a was found to match the natural product in structure and biological activity. Six related analogs 2–7 of stylissatin A were synthesized on Wang resin and characterized by spectral analysis. The natural product ( 1a ), the rotamer ( 1b ), and (d ‐allo‐Ile²)‐stylissatin A ( 1c ) exhibited significant inhibition of NO^.. Further investigations were focused on 1b , which also inhibited proliferation of T‐cells and inflammatory cytokine IL‐2 production. The analogs 2–7 weakly inhibited NO^. production, but strongly inhibited IL‐2 cytokine production compared with synthetic peptide 1b . All analogs inhibited the proliferation of T‐cells, with analog 7 having the strongest effect. In the analogs, the Pro⁶ residue was replaced by Glu/Ala, and the SAR indicates that the nature of this residue plays a role in the biological function of these peptides. Copyright © 2016 European Peptide Society and John Wiley & Sons, Ltd.     

Theoretical insights into thermal cyclophanediene to dihydropyrene electrocyclic reactions; a comparative study of Woodward Hoffmann allowed and forbidden reactions

The thermally allowed electrocyclic reaction syn-cyclophanediene (CPD) to dihydropyrene (DHP) was compared with the disallowed thermal electrocyclic reaction in anti CPD through density functional theory (DFT) calculations at the B3LYP/6-31?+?G(d) level. Moreover, the results were also compared with the electrocyclization of 1,3,5 hexatriene to 1,3-cyclohexadiene . The Woodward-Hoffmann (W-H) allowed thermal reaction in syn CPD 11 has a calculated activation barrier of 6.23 kcal mol^?1, compared with 29 kcal mol^?1 for the electrocyclization of 1,3,5 hexatriene to 1,3-cyclohexadiene. The enhanced acceleration of electrocyclization is believed to arise from geometrically enforced spatially aligned termini of the hexatriene. Substituents at the electrocyclic terminus of cyclophanediene significantly affected (up to three fold) the activation barriers. Mono-substitution of CPD has substituent dependent acceleration or deceleration whereas di-substitution always increased the activation barrier. The activation barrier for electrocyclization in 33 is 4.44 kcal mol^?1, which is the lowest activation barrier for any thermal electrocyclic reaction. Cyclophanedienes (CPDs) substituted with electron-rich substituents cyclized with high activation barriers and vice versa, a phenomenon significantly different from electrocyclic reaction of 1,3,5-hexatriene where no such trend is traceable. Comparison of W-H allowed and forbidden electrocyclization in syn and anti CPDs, respectively, revealed quite similar electronic demand, although the transition states are different in nature. The transition state for a W-H forbidden reaction is biradicaloid, with most of the spin density at the electrocyclic termini; however, the transition state for a W-H allowed reaction has no such contribution. We also believe that this is the first study of its type, where W-H allowed and forbidden reactions are compared on a similar set of molecules, and compared for electronic effect through substituents.     

Mitochondrial Genome Analysis of Wild Rice (Oryza minuta) and Its Comparison with Other Related Species

Oryza minuta (Poaceae family) is a tetraploid wild relative of cultivated rice with a BBCC genome. O. minuta has the potential to resist against various pathogenic diseases such as bacterial blight (BB), white backed planthopper (WBPH) and brown plant hopper (BPH). Here, we sequenced and annotated the complete mitochondrial genome of O. minuta. The mtDNA genome is 515,022 bp, containing 60 protein coding genes, 31 tRNA genes and two rRNA genes. The mitochondrial genome organization and the gene content at the nucleotide level are highly similar (89%) to that of O. rufipogon. Comparison with other related species revealed that most of the genes with known function are conserved among the Poaceae members. Similarly, O. minuta mt genome shared 24 protein-coding genes, 15 tRNA genes and 1 ribosomal RNA gene with other rice species (indica and japonica). The evolutionary relationship and phylogenetic analysis revealed that O. minuta is more closely related to O. rufipogon than to any other related species. Such studies are essential to understand the evolutionary divergence among species and analyze common gene pools to combat risks in the current scenario of a changing environment.     

Towards better insect management strategy: restriction of insecticidal gene expression to biting sites in transgenic cotton

Most of the commercialized Bt crops express cry genes under 35S promoter that induces strong gene expression in all plant parts. However, targeted foreign gene expression in plants is esteemed more important as public may be likely to accept ‘less intrusive’ expression of transgene. We developed plant expression constructs harboring cry1Ac gene under control of wound-inducible promoter (AoPR1) to confine Bt gene expression in insect wounding parts of the plants in comparison with cry1Ac gene under the control of 35S promoter. The constructs were used to transform four Turkish cotton cultivars (GSN-12, STN-468, Ozbek-100 and Ayhan-107) through Agrobacterium tumefaciens strains GV2260 containing binary vectors p35SAcBAR.101 and AoPR1AcBAR.101 harboring cry1Ac gene under control of 35S and AoPR1, respectively. Phosphinothricin (PPT) was used at concentration of 5 mg L^?1 for selection of primary transformants. The primary transformants were analyzed for transgene presence and expression standard molecular techniques. The transformants exhibited appreciable mortality rates against larvae of Spodoptera exigua and S. littoralis. It was found that mechanical wounding of T ₁ transgenic plants was effective in inducing expression of cry1Ac protein as accumulated levels of cry1Ac protein increased during post-wounding period. We conclude that use of wound-inducible promoter to drive insecticidal gene(s) can be regarded as a valuable insect-resistant management strategy since the promoter activity is limited to insect biting sites of plant. There is no Bt toxin accumulation in unwounded plant organs, seed and crop residues, cotton products and by-products, thus minimizing food and environmental concerns.